The present invention relates to a contact image sensor employed in facsimiles, scanners for personal computers and scanner for copy machines, and more particularly to a contact image sensor having a data line arrangement capable of inhibiting a crosstalk phenomenon between neighboring data lines for a transmission of charges generated from photoelectric converters.
Generally, contact image sensors are widely used as important elements for scanning graphics and characters in facsimiles, personal computers and electronic copy machines. Such contact image sensors should accurately transmit image information sensed to processing units without any distortion of the image information. However, since many data lines are formed in a given area in fabrication of a contact image sensor, a parasitic capacitance may be generated among the data lines. Such a parasitic capacitance generates a crosstalk phenomenon resulting in a time delay and a signal distortion. As a result, a deterioration in performance of the entire system may occur.
For solving such problems, various researches are actively in progress. Now, conventional contact image sensors proposed to solve the above-mentioned problems will be described, in conjunction with the annexed drawings.
FIG. 1 is a circuit diagram of a conventional type contact image sensor. As shown in FIG. 1, the contact image sensor comprises a photoelectric conversion unit 1 including m aligned blocks each having n aligned photoelectric converters and serving to convert an optical signal into an electrical signal so as to generate an optical carrier, and a switching unit 2 including m aligned blocks each having n aligned thin film transistors respectively corresponding to the photoelectric converters of each corresponding block of the photoelectric conversion unit 1 and serving to sequentially output optical carriers from the photoelectric conversion unit 1. The contact image sensor further comprises m gate lines 3 respectively connected in common to gate electrodes of all thin film transistors of the same numbered blocks of the switching unit 2 and adapted to apply gate drive signals to the thin film transistors, n data lines 4 respectively connected in common to drain electrodes of the same numbered thin film transistors of the blocks of the switching unit 2 and adapted to transmit optical carriers outputted from the thin film transistors, a bias line 5 connected in common to all photoelectric converters of the photoelectric conversion unit 1 and adapted to apply a bias signal for a photoelectric conversion to the photoelectric converters, m gate line pads G.sub.1 to G.sub.m respectively connected to the same numbered gate lines 3, n data line pads D.sub.1 to D.sub.n respectively connected to the same numbered data lines 4, and a bias line pad C connected to the bias line 5.
Operation of the conventional type contact image sensor will be described.
Each of photoelectric converters of the photoelectric conversion unit 1 converts an optical signal into an electrical signal having a current intensity determined by the intensity of the optical signal, thereby generating an optical carrier.
As a bias signal of -5 V is applied to all the photoelectric converters via the bias line 5 and drive signals for thin film transistors are sequentially applied to the blocks of the switching unit 2 via the gate lines 3, all the thin film transistors of each block of the switching unit 2 receiving each corresponding drive signal are simultaneously turned on. As a result,the optical carriers generated from the photoelectric converters of each block are separately outputted via n data lines 4, respectively.
For example, when a high level signal is applied in common to the thin film transistors of the first block B.sub.1 of the switching unit 2, the thin film transistors of the same block are simultaneously turned on, thereby causing the optical carriers from the corresponding photoelectric converters to be separately outputted via n data lines 4, respectively.
The above procedure is sequentially repeated until the last block of the switching unit 2 is driven. Thereafter, 0 V is applied to the bias line 5 so that the photoelectric conversion unit 1 can receive optical signals again to generate optical carriers.
However, this conventional type contact image sensor has problems of an undesirably narrow space and a severe overlap between neighboring data lines in a case of n&gt;m, because at least n data lines are provided in a given region. Furthermore, a large overlap occurs between data and gate lines. Due to such problems, a parasitic capacitance is generated between the data lines or between the data and gate lines, thereby resulting in a crosstalk phenomenon causing a signal delay. As a result, scanning and processing rates of data communication terminal equipments are adversely affected. Moreover, a deterioration in resolution occurs.
For solving the above-mentioned problems, there has been proposed an alternative type contact image sensor developed by Simens Company, Germany. Referring to FIG. 2, there is illustrated an example of such an alternative type contact image sensor. In FIG. 2, elements corresponding to those in FIG. 1 are denoted by the same reference numerals.
The contact image sensor of FIG. 2 has the same arrangement as that of FIG. 1, except for gate lines and data lines. In other words, the alternative type contact image sensor comprises a photoelectric conversion unit 1 including m aligned blocks each having n aligned photoelectric converters, a switching unit 2 including m aligned blocks each having n aligned thin film transistors respectively corresponding to the photoelectric converters of each corresponding block of the photoelectric conversion unit 1, n gate lines 3 respectively connected in common to gate electrodes of the same numbered thin film transistors of the blocks of the switching unit 2, and m data lines 4 respectively connected in common to drain electrodes of all thin film transistors of the same numbered blocks of the switching unit 2, as shown in FIG. 2.
Operation of the alternative type contact image sensor will be described.
Each of photoelectric converters of the photoelectric conversion unit 1 converts an optical signal into an electrical signal having a current intensity determined by the intensity of the optical signal, thereby generating an optical carrier.
As a bias signal of -5 V is applied to all the photoelectric converters via the bias line 5 and drive signals for thin film transistors are sequentially applied to the blocks of the switching unit 2 via the gate lines 3, the same numbered thin film transistors of all blocks of the switching unit 2 receiving corresponding drive signals are simultaneously turned on. As a result, the optical carriers generated from the photoelectric converters of the blocks are separately outputted via m data lines 4, respectively.
For example, when a high level signal is applied in common to the first thin film transistors of the blocks of the switching unit 2, the first thin film transistors are simultaneously turned on, thereby causing the optical carriers from the corresponding photoelectric converters to be separately outputted via m data lines 4, respectively.
The above procedure is sequentially repeated until the last thin film transistor of each block of the switching unit is driven. Outputting of optical carriers through each data line 4 is sequentially carried out in the order from the first photoelectric converter of each corresponding block to the last photoelectric converter.
Although this alternative type contact image sensor solves the problem of the overlap between neighboring data lines encountered in the afore-mentioned conventional type contact image sensor, it has a problem of a severe overlap between neighboring gate lines in a case of n&gt;m. Furthermore, the data lines may have different lengths due to different positions of thin film transistors of the switching unit 2. Consequently, this alternative type contact image sensor solves insufficiently the problems encountered in the conventional type contact image sensor.
For solving the above-mentioned problems, there has been also proposed a contact image sensor having a meadering type data line arrangement developed by Fuji Xerox Company, Japan. Referring to FIG. 3, there is illustrated an example of such a meadering type contact image sensor. In FIG. 3, elements corresponding to those in FIG. 1 are denoted by the same reference numerals.
The contact image sensor of FIG. 3 has the same arrangement as those of FIG. 1, except for data lines. In other words, the meandering type contact image sensor comprises a photoelectric conversion unit 1 including m aligned blocks each having n aligned photoelectric converters, a switching unit 2 including m aligned blocks each having n aligned thin film transistors respectively corresponding to the photoelectric converters of each corresponding block of photoelectric conversion unit 1, m gate lines 3 respectively connected in common to gate electrodes of all thin film transistors of the same numbered blocks of the switching unit 2, and n data lines 4 respectively connected in common to drain electrodes of the same numbered thin film transistors of the odd-numbered blocks of the switching unit 2 and drain electrodes of the reversely-same numbered thin film transistors of the even-numbered blocks of the switching unit 2 in a manner that drain electrodes of the first thin film transistors of the odd-numbered blocks are connected with drain electrodes of the last thin film transistors of the even-numbered blocks while drain electrodes of the last thin film transistors of the odd-numbered blocks are connected with drain electrodes of the first thin film transistors of the even-numbered blocks, as shown in FIG. 3.
Drive signals for thin film transistors are sequentially applied to the blocks of the switching unit 2 via the gate lines 3, the optical carriers generated from the photoelectric converters of each block are separately outputted via n data lines 4 in a sequential manner, respectively.
Although this meandering type contact image sensor solves the problem of the overlap between neighboring data lines encountered in the afore-mentioned conventional type contact image sensor, it encounters design and manufacture difficulties because each data line must be designed to pass between adjacent picture elements. As a result, it is difficult to obtain a high resolution in the meandering type contact image sensor. Furthermore, since the length of each data line is extremely long, the data line resistance is increased, thereby resulting in a decrease in transmission efficiency.